I will arrive at ZRH on US 767 from PHL and I will have 4 hours until my connecting flight on Swiss Intl. Last time I flew thru ZRH in 2001 and I don't know if anything has changed. What are my best options to get few hours of spotting time?
Is observation deck a good option in the morning?

defenetely .. observationdeck the light is good till around 12:00. You could also walk to P6 take the elevator to the highest floor and walk to the end, there you can take all the lineups for rwy 28. Light good from morning till the end.

I'd definitely stay with the observation deck for the limited time you have. There's food and drinks available, shelter during rain (or sun), and departures of heavy aircraft on rwy 16 (the one passing by the obs deck at terminal B) will be plenty from mid-morning until around 2pm.